Systemd first boot with rw rootfs

[Gylstorff Quirin <quirin.gylstorff@siemens.com>]

Hi all,


currently we trigger a first boot by removing the machine-id from the
root file system[1]. In case of a writable root filesystem systemd will 
enable all units in /usr/lib/systemd/system with the vendor preset 
enable. This will also enable units in /usr/lib/systemd/system which are 
disable during the installation like ssh.socket[2].

This will not happen in a Debian installation as first boot is the 
installation boot as defined by:
"For normal operating system installations, where a custom image is 
created for a specific machine, /etc/machine-id should be populated 
during installation."[3]


If a first boot is not detected, e.g. by using an empty /etc/machine-id, 
the units are started as defined during the installation [4].

Another possibility is to mask the units during the the installation.

[1]: 
https://github.com/ilbers/isar/blob/49854b625a6b0dc9339a33c3b4d78b2ce418b377/meta/classes/image-postproc-extension.bbclass#L57
[2]: https://gitlab.com/cip-project/cip-core/isar-cip-core/-/issues/48
[3]: 
https://manpages.debian.org/bullseye/systemd/machine-id.5.en.html#INITIALIZATION
[4]: 
https://manpages.debian.org/bullseye/systemd/machine-id.5.en.html#FIRST_BOOT_SEMANTICS
-- 


With best regards,
Quirin Gylstorff

Siemens AG
Technology